[Intel-gfx] [PATCH] drm/i915: Implement workaround for DP2 UHBR bandwidth check

[Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>]

According to spec, we should check if output_bpp * pixel_rate is less
than DDI clock * 72, if UHBR is used.

HSDES: 1406899791
BSPEC: 49259

v2: - Removed wrong comment(Rodrigo Vivi)
    - Added HSDES to the commit msg(Rodrigo Vivi)
    - Moved UHBR check to the MST specific code

Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp_mst.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index 8b0e4defa3f1..1f1f7f5f6501 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -339,10 +339,19 @@ static int intel_dp_mst_compute_config(struct intel_encoder *encoder,
 		ret = intel_dp_dsc_compute_config(intel_dp, pipe_config,
 						  conn_state, &limits,
 						  pipe_config->dp_m_n.tu, false);
-	}
+		if (ret < 0)
+			return ret;
 
-	if (ret)
-		return ret;
+		if (intel_dp_is_uhbr(pipe_config)) {
+			int output_bpp = pipe_config->dsc.compressed_bpp;
+
+			if (output_bpp * adjusted_mode->crtc_clock >=
+			    pipe_config->port_clock * 72) {
+				drm_dbg_kms(&dev_priv->drm, "DP2 UHBR check failed\n");
+				return -EINVAL;
+			}
+		}
+	}
 
 	ret = intel_dp_mst_update_slots(encoder, pipe_config, conn_state);
 	if (ret)
-- 
2.37.3